Hybrid thermoplastic composite beam structures integrating UD tows, stamped fabrics, and injection/compression moulding

To investigate thermoplastic composite structures combining multiple material forms and processing techniques, a generic beam tool was developed that enabled over-moulding of stamped fabrics and robotically placed unidirectional tows (UDtow). Beams produced from different material and process combinations were tested in flexure. Compared with a glass mat thermoplastic (GMT) beam, the maximum force for ‘free-free’ and ‘fixed-fixed’ end conditions was respectively increased by: 30% and 242% for GMT/UDtow, 69% and 224% for GMT/fabric, and 79% and 460% for GMT/UDtow/fabric. Compared with a plain short glass fibre injection moulded (IM) beam, the maximum force for ‘free-free’ and ‘fixed-fixed’ end conditions was respectively increased by: 26% and 213% for IM/UDtow, 64% and 286% for IM/fabric, and 63% and 411% for IM/UDtow/fabric. Standard in-mould cycle times and tool temperatures (50C) were used. The fabric over-moulding process window was examined in detail. The fabric preheat temperature dominated the process. Both global beam testing and coupon-based testing showed that the average interfacial temperature between the fabric insert and the over-moulded material at the moment of contact needed to be above the melt temperature of the polymer. The inserts did not need to be heated above melt temperature, thereby maintaining integrity during the high pressure over-moulding processes.